Extracapsular cataract extraction involves the removal of the lens nucleus from the eye of a patient. Commonly an incision is made in the anterior capsule, and the clouded lens tissue contained within the capsule is removed; the posterior capsule and peripheral portions of the anterior capsule (the "anterior capsule flaps") are left intact. An artificial intraocular lens may then be implanted in the eye, the lens being supported in either the anterior or posterior chamber and being positioned by wires or other structure that extend from the lens outwardly into contact with supportive, circumferential tissue adjacent the iris.
Typical intraocular lenses are disclosed in the following references:
U.S. Pat. No. 4,092,743 (Kelman);
U.S. Pat. No. 4,174,543 (Kelman);
U.S. Pat. No. 4,244,060 (Hoffer);
U.S. Pat. No. 4,261,065 (Tennant);
U.S. Pat. No. 4,328,595 (Sheets);
U.S. Pat. No. 4,338,687 (Rainin);
U.S. Pat. No. 4,340,979 (Kelman);
U.S. Pat. No. 4,343,050 (Kelman);
U.S. Pat. No. 4,370,760 (Kelman);
U.S. Pat. No. 4,412,359 (Myers).
Intraocular lenses in general are characterized by including a central lens or lenticular portion, and two or more struts, usually radially resilient, that extend outwardly of the lens and which gently but elastically engage appropriate circumferential eye structure adjacent the iris. The struts of intraocular lenses that are to be employed in the anterior chamber of the eye commonly are supported in the angle formed between the iris and the internal periphery of the cornea, avoiding substantial contact or interference with the trabacular meshwork. Intraocular lenses intended to be mounted in the posterior chamber commonly have struts or other fixation devices that engage the ciliary recess or the periphery of the posterior lens capsule that remains after removal of the lens nucleus.
Occasionally after cataract surgery and placement of an intraocular lens within the eye, it becomes necessary to perform a posterior capsulotomy to alleviate cloudiness of the posterior capsule which frequently develops over time after cataract surgery. Such cloudiness is generally due to the growth of lens fibers or capsular fibrosis. Some recent studies have indicated that the growth of lens fibers or capsular fibrosis may be caused by cells on the intact anterior capsule flaps migrating toward and/or contacting the posterior capsule. Historically, the cloudiness was removed by performing a discission; a small knife was inserted behind the intraocular lens and used, under a microscope, to trim away the clouded portion of the posterior capsule.
With the development of modern laser technology it is now possible to perform a posterior capsulotomy without surgically entering the eye by use of a laser beam focused upon the posterior capsule. A number of small holes are made in the capsule in a number of locations until the center portion has been removed, providing a clear "window" for unobstructed light to pass through the lens rearwardly to the retina. A popular laser for use in this technique is the "YAG" laser (Yttrium-aluminum-garnet).
If the intraocular lens is mounted in the posterior lens capsule, however, the lens commonly lies in face-to-face contact with the anterior surface of the posterior capsule. When a laser is focused on the posterior capsule, local intense heating occurs which may shatter or otherwise damage the lens.
One solution which has been offered to alleviate this problem is to include a posteriorly projecting ring on the posterior surface of the intraocular lens body to space the posterior capsule of the eye from the confronting lens surface. Such rings are disclosed in U.S. Pat. Nos. 4,244,060 (Hoffer), and 4,412,359 (Myers).
Such rings on the lens body have at least two disadvantages, however. First, they are optical aberrations on the lens, not only diffusing the light rays passing through the lens, but also causing distracting reflections of light within the eye. These problems are particularly acute when the iris is dilated, and may be exascerbated if the lens is not perfectly centered. Secondly, depending upon the physical dimensions, placement, and orientation of the lens, such rings may inhibit the ability of a physician to properly examine peripheral portions of the retina. Such examinations are important to the diagnosis of various eye disorders including retinal detachments, retinal holes or tears, tumors, cysts, and so forth.